Vibratory system and method



Feb. 12, 1935. w PlERCE Re. 19,461

VIBRATORY SYSTEM AND METHOD Original Filed Jan. 3. 1927 4 Sheets-Sheet 1 f Z780 Z230 2300- 2310 6 601 eldPi-azwe 2200 zzao 2300 2310 attorney Feb. 12, 1935. G. w. PIERCE VIBRATORY SYSTEM AND METHOD Original Filed Jan. 5, 192"! 4 Sheets-Sheet 2 attorney Feb. 12, 1935. I WPIERCE Re. 19,461

VIBRATORY SYSTEM AND METHOD I Original Filed Jan. 3, 1927 4 Sheets-Sheet 3 9. 10. l L! I I71 U6 27 to 7 6 60736 lllfliei'ca y atio rfifig Feb. 12,1935. G, w, MERGE v Re. 19,461

VIBRATORY SYSTEM AND METHOD ori inal Filed Jan. 3, 1927 4 Sheets-Sheet 4 Reiesued Feb. 12, 1935 ;19 451 UNITED STATES PATEN ILOFFICE George W. Pierce, Cambridge, Mass.

Original No. 1,750,124, dated March 11, 1930, Serial No. 158,452, January 3, 1927. A'pplication for reissue June 26, 1931, Serial No. 547,131

22 Claims. (Cl. 250-36) The present invention relates to vibratory The invention will beexplained in greater desystems and apparatus, and more particularly tail in connection with the accompanying drawto systems and apparatus for producing, sustainings, in which Fig. 1 is a diagrammatic view of ing, transmitting, receiving, and the like, elecapparatus and circuits constructed and arranged trio, magnetic and mechanical oscillations. From to illustrate the principle of the present inven- 5- a still more limited aspect, the invention relates tion; Figs". 2 and 3 are plots of experimental to the frequency control and the frequency results; ,Flg. 4 is a-diagrammatic view similar to stabilization of the electric oscillations of electric Fig. 1,,illustrating the invention as applied to a circuits, and to the transfer of periodic, electric vacuum-tube oscillator for producing sustained energy from one electric system to another. vibrations and alternating currents; Fig. 5 is a 10 According to the specific embodiments of the similar diagrammatic view, illustrating the sysinvention hereinafter described and illustrated tem of Fig. 4 in connection with an amplifier for in the accompanying drawings, these results are supplying a load; Fig. 6 is a similar view, illusobtained by the interaction between the electric" trating one of the coils in the input circuit and circuit or circuits and a mechanically vibrating the other in the output circuit of a resistance- 15 core member of novel construction the mecha'ncondenser-coupled amplifier unit of two tubes; ical vibrations of which control the frequencies Fig. 7 is a section of a vibrator particularly deof the electric oscillations of the electric circuit signed for producing sound in water, the section or circuits. being taken upon the line 'l7 of Fig. 8, look- Electromechanical vibrators for bringing about ing in the direction of the arrows; Fig. 8 is an 20 such results are not, broadly, new. Piezo-elecelevation of the same; Figs. 9 and 10 are views tric crystals are admirably adapted for this pursimilar to Figs. 7 and 8, respectively, of a modipose. The use of such crystals, however, involves fication; Fig. 11 is a diagrammatic cross-section certain disadvantages. In the first place, they of a ship, showing a vibrator spanning the hull 5 are quite expensive and laborious to make and thereof to produce sound in the water by operin the second place, there is always danger that atlon through the ships plates; Fig. 12 is a a little extra load will cause the crystal to bediagrammatic view of a vibrator for producing come shattered, destroying, in a fraction of a sound vibrations in the air; Fig. 13 is a diagramsecond, a comparatively costly instrument that matic view of a transmitting-and-receiving sysrequire a long time to produce. To avoid this tern according to the present invention; and 30 result, complications must be resorted to, but Fig. 14 is a diagrammatic view illustrating the these, in turn, impair the eificiency of operation vibrator mounted in a vacuum. and there are also other disadvantages. A core 2 is shown axially positioned within an The novel vibrator of the present invention has inductive and resistive field coil, indicated in none of these disadvantages and, furthermore, various figures by thenumerals 10, 22 and 24. 35 it operates upon an entirely difierent principle. The core 2'may be in the form 0. a tube, or a It is adapted, when stimulated magnetically, as rod, and may freely rest centrally upon a support by means of an electromagnetic field, to become 6, as shown in Figs. 5 and 6,,or it may be cenvery slightly mechanically deformed or distorted trally clamped between the support 6 and a by magnetostriction. The resulting increment of -second clamping member 8, as illustrated in 40 deformation may be a lengthening, or a shorten- Figs. 1 and 4, or it may be otherwise supported, in or m other distortion, depending n theas shown in other figures. When an electric material and on the polarity of the increment of current is passed through the coil, a magnetic the magnetic field. Conversely, when the vifield will be established that will cause mechanbrator is mechanicallydeformed or distorted, it ical distortion or deformation of the core 2 by will react or respond magnetically by magnetomagnetostriction. This action of the magnetic.

striction with an increment of magnetization defield upon the core 2 will, for brevity, be hereinpending upon the nature of the preexisting after termed stimulation. Conversely, any magnetic field and the mechanical deformation. mechanical deformation or distortion of the core Both with the novel vibrator of the present inwill cause a magnetostrictive reaction upon the vention and .with piezo-electric crystals, the electromagnetic field, and this will have its effect mechanical deformations are produced by excitupon the electric current or voltage in the coil. ing reversible internal stresses in the core, and This reaction will, for brevity, be hereinafter rethe core readily recovers upon the withdrawal ferred to in the specification and the claims as or the deforming forces. e the "response.

' If the current or voltage is alternating, the electromagnetic field created thereby/ will also be alternating. The core 2 will, therefore, increase and decrease in length (let'us say) many times a second, every variation in the current producing its stimulative effect on the core 2, and every deformation ofthe core producing its reaction response upon the current. The core 2 will, in consequence, freely vibrate mechanically by magnetostriction about a nodal point at its center with a period of vibration equal to the period of the alternating electromotive force. Ordinarily, these vibrations, will be quite small. When the alternating frequency is close to, or substantially the same as, the natural frequency of me-,

chanical vibration of the core 2, however, the amplitude of vibration of the core, though still small, becomes relatively quitelarge. The core will then react inductively on the load to render its consumption of power criticalas to frequency for frequencies near the free frequency of the core. The mechanical damping of the core, mounted as shown, is as small as possible, with the result that the resonant response of the core is very sharp and pronounced. Of course, there will usually be more than one specific frequency of magnetization at which the core will thus resonate, as is explained hereinafter.

In Fig. l, the magnetostrictive core 2 is shown driven by a solenoid coil 10, provided with conductors 12 and 14 by which it may be connected, for simplicity, in series with a source of alternating electromotive force, such as an alternatingcurrent generator 16. Other, more complicated, sources of alternating current are illustrated in other figures.

Alocal battery 18 (shown in Fig. 1 in series with the source 16 and the winding 10) applies a steady magnetizing field t the core 2, over which the alternating field produced by the generator 16 i is superposed. The alternating field is preferably smaller than the steady field, in order that the combined fields may not, at any time fall to zero. The battery may be dispensed with, and the core may be magnetized electromagnetically by a local source, or it may be permanently magnetized, instead, or the battery and a permanently magnetized core may be employed together.

In order not to complicate the showing of Fig. 1, no means are illustrated therein for tuning the circuit or varying the frequency of the alternating current flowing therein, particularly as the core 2 may itself be a tuned element of very low decrement, thereby dispensing with or supplementing electrical tuning of the circuits. It will be understood that a tuning condenser or other tuning device may be used, thereby attaining greater sensitiveness and selectivity. If the frequency of the alternating current is varied gradually by this tuning device, or by variation of the speed of the generator, from'a value on one side of the natural or resonant frequency of mechanical vibration of the core, to a value on the other side of this frequency, acomparatively intense sound is produced somewhere in this range, if

the resonant frequency is within audible limits. If the frequency is outside the audible range, the resonant response is made manifest by a transient sound, or click, in the telephones, or by a change in the reading of an ammeter 20 connected in circuit. This resonant response takes place whenever the tuning of the electromotive force passes through values synchronous with the period of the vibrator, setting the vibrator into violentvi brations; or, in more technical language, the apof the system. The invention, therefore, finds one application as a very accurate [frequency meter or indicator which forms the subject matter of a divisional application, Serial No. 272,033, filed April 23, 1928, which matured, on October 11, 1932, into Letters'Patent No. 1,882,395. By filing the resonator down, or adding to its mass by solder or plating, any desired frequency may readily be attained, either high or low, and the frequency meters calibrated accordingly. Once calibrated by comparison with a standard frequency meter, they will then serve as very accurate meters themselves. Further illustrations of this operation will appear in connection with a discussion of the other figures of the drawings.

The operation will be better understood in connection with the plot of Fig. 2, showing the relation between the resistance R and the reactance Lw of the winding 10 for different frequencies of applied electromotive force in the neighborhood of the natural or free frequency of the core. The axis of abscissa: represents the applied frequency 1 (number of cycles per second) of the electromotive force, and the ordinate is, in the case of one curve, the reactance Lu, and in the other, the resistance R, both measured in ohms. w is an abbreviation for 2w). The particular core employed in the experiment was of nickel-steel, about 0.92 cm. long, and had a free frequency of fundamental longitudinal vibration of about 2,290 cycles per second. As the curves of Fig. 2 clearly show, the reactance Leo and the resistance R undergo marked effects, the former sinking to a minimum in the neighborhood of the resonant frequency of the core, and the latter at a frequency somewhat greater.

In Fig. 3, the total impedance Z of the winding 10 is similarly plotted against the applied frequency f of the electromotive force. The values of Z shown in this plot were obtained by taking the square root of the sum of the squares of the resistance R. and the reactance Lw of Fig. 2. According to this plot, the impedance Z of the winding 10 is at a minimum at a frequency of about 2,291 cycles per second. The ammeter 20 in the circuit of Fig. 1 will therefore indicate a maximum of current when the generator frequency has this value.

In the neighborhood of this resonant frequency, the power output of the generator undergoes a large increase. Assuming, therefore, that the generator is running at a speed a little too slow to give maximumpower, and that the generator increases in speed, the draft of power from the generator by the load will increase, and tend to slow the generator down. If, on the other hand, the generator speed tends to decrease, the load will decrease also, and this will tend to maintain the generator speed high. The vibration of the magnetomechanical vibrator thus acts to stabilize the generator, and a second application of the invention, therefore, is to stabilize the frequency of an alternating-current system. By using a sufficiently massive magneto-mechanical vibrator, with a correspondingly large impedance in the circuit, this stabilizing effect may be made very large. v

Any material having suitable properties may, of course, be used for the vibrating body 2, but it should obviously be constituted of material that is suitably magnetizable. A simple rod or tube of the proper material will operate; but to obtain the best results, depending upon-the purpose for which the apparatus is used, the core should be characterizedby comparatively large magnetostrictive effects and comparatively low vibrationa1 decrement. Such effects exist in'magnetic metals and magnetic alloys. Different bodies possess the requisite properties in different degrees. Alloys containing nickel, chromium and iron, in proper proportions, have comparatively large magnetostriction; Ordinary metals have their elasticity and density slightly modifiable by changes in temperature. Such temperature changes, therefore, introduce small variations in the natural period of mechanical vibration of such bodies. To obtain substantially. constant frequency, it is preferred to utilize a vibrator having a coeflicient of the ratio of elasticity to density that variesas little as possible with variation of temperature. Certain alloys of iron, nickel and chromium are .known to possess substantially constant coeflicients of frequency with variations of temperature. One such alloy, constituted of 52 percent iron, 36 percent nickel and 12 percent chromium, is practically independent of temperature. I have found that a rod of nickel,

. chromium and iron has a period that is also practically independent of magnetic field strength over wide limits. Cores of nickel, nickel steel and chrome steel have large magnetostrictive effects. Annealed rods, according to my experiments, give the best results.

If high precision of frequency is desired, the metal should have a high constancy of elasticity. If great sensitiveness, rather than high precision, is the aim, the metal may have less constancy of elasticity, but higher sensitivity.

If the vibrator is in the form of a rod or tube of small diameter, the period of vibration is nearly: proportional to the length of the rod or tube. Thus, a rod offnickel-steel, known in the trade as Stoic metal, having a diameter of onehalf centimeter and a length of ten centimeters, has a fundamental period of longitudinal vibration of about 1/2l,000 of a second. A rod of the same diameter ten times as-long (100 centimeters) has a period about 1/2100 of a second. Rods of the same diameter and the same two respective lengths, but constituted of an alloy of iron and chromium in a particular proportion, have the fundamental periods of 1/27,000 and 1/2'700 of a second, respectively. These results are consistent with the fact that the two materials have different elasticities and densities.

The above figures correspond to but a single mode of vibration of the cores. But all vibratory bodies have also additional modes of vibration. In addition to one or more natural fundamental frequencies of mechanical vibration, the core has also frequencies of vibration determined by the operation of the core in halves, thirds, fourths, fifths and other overtones. There will usually, therefore, be more than one specific frequency of magnetostriction at which the core will resonate as above described. Such other modes of vibration may be produced by particular methods of stimulating the vibrations, or by particular modes of clamping the body. In addition to other modes of longitudinal vibration, there are certain magnetostrictive effects attendant upon the twist or torsion of the cores, particularly if current be sent lengthwise through the core, so that torsional vibrations are also available. All these modes and kinds of vibration may be utilized according to the present invention.

And, of course, it will be understood that the,

invention is not restricted to the use of vibrators in the form of rods or tubes. The magneto-mechanical vibrator of the present invention may, for example. be constituted of a rod with heavy weights attached to the ends thereof, as shown in Fig. 1. This will effectively decrease its period of vibration to a'compar'atively low frequency.

As a further example, the vibrator may be constituted of a bundle or a plurality of small rods or wires embedded as a unit in a highly elastic insulating and binding material, or attached together by solder or by welding in suitable spots,

will cause the vibrator to vibrate energetically and thus transmit energy to the other circuit. Thus, in the system of Fig. 4, the core 2 is positioned axially of a magnetic field, h re shown as produced by coils 22 and 24, and is preferably held in such manner, as by means of the cen trally positioned-clamps 6 and .8, as freely to vibrate longitudinally about a nodal point at its center. For symmetry, one of the coils is positioned on one side of the middle. of ihe core 2 and the other on the other side. The coils may be compacted near the center of the core, or they may be separated or spread out, each over the whole region of the half-length of the core, or they may be replaced'by a single coil. The coil 22 is connected, in series with the local battery 18, between the filament or cathode 26 and the plate or anode 28, in the output or plate circuit of a vacuum tube 30. The coil 24 is similarly connected in the input or gridcircuit of the tube,

between the filament 26 and the grid or third electrode 32. The coils 22 and 24 thus form electrical paths between the, filament and the plate, and between the filament and the grid, respectively. The grid and the plate may, if desired, be spanned by a variable condenser 34; or the tuning condenser may be connected in parallel with one or the other of the coils 22 and 24; or, if the coils are Suitably designed, the condenser may be omitted altogether. An electric vacuum-tube oscillator is thus provided, having considerable similarity to oscillators of the prior. art. The new oscillator, however, comprises a very important novel feature in the transformer for coupling the input circuit and the output circuit together, and comprising the coils 22 and24 and the mechanically tuned core of magnetizable material for transforming resonant electric energy and feeding it from the output circuit to the input circuit. tion of energy is effected, at constant frequency, through the effects produced by the distortion or deformation of the core, as will presently be larger and more stable and-preventing parasitic electric oscillations by electric feed back, and of This transformarestricting the oscillations to periods determined by the mechanically-tuned core.

The system of Fig. 4 may be operated somewhat as follows: For certain settings of the condenser, the system will, or may be oscillatory in itself; that is, it will oscillate at variable frequency, like any other system of like construction and arrangement, and entirely independently of the core. When, however, the setting of the condenser corresponds to a frequency approximating the natural frequency of the core, the frequency of the alternating current will fall into step with the frequency of the core, and the core will begin to vibrate. When this happens, the condenser may be varied over a comparatively wide range, or even removed altogether, without materially modifying the frequency of the alternating current and the system will oscillate at a frequency determined by the frequency of mechanical vibration of the core 2. Here the core acts as a stabilizer of the frequency, the frequency of the Oscillations being substantially .constant and equal to the natural frequency of mechanical vibration of the core.

Or, the system may operate as follows: Let it be assumed that the magneto-mechanical vibrator is held or damped so as to prevent its vibrations, and that the circuits are so arranged that the system will not oscillate under such conditions. This may readily be effected by preventing feed back between the coils 22 and 24 due to their opposed winding, or their small mutual inductance, or because of their high losses brought about by the presence of the magnetizable core, or because of the condenser setting, or for other reasons. With the core in this damped, immobile state, there is no tendency for vibrating currents to appear in the system. Let the damping of the core be now removed. As soon as the core is free to vibrate, its compression following upon a small disturbance, generates an electromotive force in the grid coil 24. This starts a variable current in the plate coil 22 and further stimulates the core. The magnetization of the plate coil causes the core to lengthen, or shorten, or twist, or become otherwise distorted. This distortion is transmitted along the core to the other half of the core,the half that started the disturbance.where it develops a change of magnetization and consequently generates a further electromotive force in the grid coil (assuming a proper design of the circuits). This dual role thus played by the core causes the core to vibrate and the otherwise non-oscillatory system to oscillate and sustain the oscillations at a frequency determined by the frequency of mechanical vibration of the core. The core here actually produces the oscillations by its cooperation with the system. It is characteristic of the system that very small changes of frequency can be brought about only by very large modifications of circuit constants.

Itis not essential that a vacuum tube be employed to produce oscillations, as is explained in application Serial No. 272,032, filed April 23, 1928, which matured, on June 12, 1934, into Letters Patent No. 1,962,154.

Of course, the operativeness of the invention does not depend upon the theories that may be advanced'to explain it, and such theoretical excoil, and with the proper phase for stimulating continuous oscillations, coils of the proper character must be connected in the circuit in the proper direction, and the condenser may need to be properly adjusted. Whether the coils 22 and 24 should be wound in one direction or the other depends-on the mutual capacity of the coils and on the lag of magnetization with respect to the magnetizing force, and may be determined by experiment with given materials.

. Illustrative of the constants employed; let us take the case of frequencies as low as 600 per second, with weighted rods, and the case of frequencies as high as 51,000 per second, with unweighted rods 4 centimeters long and 5 to '1 millimeters in diameter. GOO-cycle frequency had about 5 henries inductance each, when measured with no iron at the core, and those used at 51,000 cycles had about 0.03 henries inductance each, without iron. To extend the range to higher or lower frequencies, it is merely necessary to adjust the coils and the dimensions of the vibrator. By proper choice of length and other dimensions, the apparatus is applicable to systems of high or low frecuency within a range that may extend from a hundred cycles to hundreds of thousands of cycles.

The novel transformer described above constitutes the subject matter of a divisional application, Serial No. 264,222, filed March 23, 1928, which matured, on October 11, 1932, into Letters Patent No. 1,882,396. This transformer may 'bbviously be used to transfer energy between other circuits than the input and the output circuits of the vacuum tube illustrated in Fig. '4. The me- The coils used at the chanical vibration of the core may be utilized as a source of energy for this purpose,-for example, as a source of sound; or the electrical alternating currents may be utilized,for example, to induce electromotive force in some other, circuit or coil brought up near to, or wound about, the coil 22. It will also be clear that, instead of the fundamental frequency, any harmonic of the result-* ant electrical oscillations may be utilized; and, vibrations other than the fundamental longitudinal frequency of the core may also be employed.

The energy from the output circuit may be transmitted to an amplifier 36, as shown in Fig. 5, in any desired manner, as by capacity coupling and the amplified current in the output circuit of the amplifier may be supplied to any desired load 38. The potential drop in the coil 22 may be utilized to act upon the grid-filament path of the amplifier 36 through a blocking condenser 37. The load may be any device requiring periodic current, such as a wireless transmitting station, a carrier or other telephone line, a motor, a sound radiator, a lamp,- a Geissler tube,a revolution counter, a clock mechanism, etc. Thus, a clock may be driven at a low frequency of 1,000. A motor may suitably be synchronized at this or any other frequency. In wired-wireless work, the oscillator may produce a carrier wave of, say, 20,000 to 45.000 cycles. The amplified energy may be transmitted to the load, either directly, or, as illustrated, through a transformer 40, 42. The energy may be further amplified, before it is utilized, by means of a further amplifier tube. The primary coil 40 of the transformer isshown in the plate circuit of the amplifier 36, and the secondary coil 42 is shown connected with the load 38. The amplifier 36 is illustrated as of the vacuum-tube type, comprising three electrodes, namely, a filament 44, a grid 46 and a plate 48. A grid-leak resister or reactor is illustratedat 50 and a biasing battery 'at.52.- The battery 18 is utilized as a 4 source of plate-current supply for boththe. tubes v the plate circuit of the tube 30, as before described,

but the coil 24 is in the grid circuit of the tube 56. The oscillations are produced by the cooperation of the vibrator with the two tubes 30 and 56. The vibrator communicates its own naturalperiod voltageimpulses to the coil 24 in the grid circuit of the tube 56 and receives impulses of the same frequency from the coil 22 of the other tube. Condensers, not shown, :may be connected about either of the coils, or from the plate terminal of one coil to the grid terminalof the other coil. This arrangement produces enhanced sensitiveness, or limits the effects'so that the tubes are not overloaded.

The presentinvention is further adapted, as a sonic oscillator, for the production and reception ofsounds of any desired frequency, particularly high frequencies. for communicating through water or other dense media. A plurality of tubes or rods 2 of highly magnetostrictive material are shown attached to one or more sound-radiating faces 58, Figs. '7 to 10. The cores 2 are surrounded by coils 22 that may be connected together, either in parallel or in series, as desired, and through which are passed an actuating periodic current superposed overa magnetizing direct current, as before described- The fields of adjacent coils are preferably reversed so that the lines of force go to the right through one set of cores and to the left through the alternately placed set of cores. The magnetizing current may be passed through auxiliary coils, if desired. The cores are preferably free from contact with the coils, so as to reduce friction, which prevents free vibration. The

mechanical system is tuned to the desired frequency, in the medium in which it is to be used. The chamber in which the coils are contained is sealed against the entry of water when submerged, as by means of a yielding band 60.

In the modification of Figs. 9 and 10, one of the radiating faces is constituted of the free ends of the rods, each having a small cap-plate 62.

According to the modification of Fig. 11, the magnetostrictive core 2 is attached to the inner opposite sides 64 and 66 of a ship. These sides will themselves act as sound radiators through the water when a properly tuned, alternating current is sent through the coils 22. Here the frequency will be low, as for audible signalling. As before explained, the magnetostrictive element shouldbe polarized by a direct-current battery, or through an auxiliary winding.

The invention is, of course, equally adapted for producing sound vibrations in the air so as to constitute a loud speaker. Sound-radiating wings for this purpose are illustrated at 68 and 70 in Fig. 12. These may be parts of a sounding box, properly shaped, proportioned and mounted for quality. The rod or wire 2 is preferably conrents.

nected to the wings 68 and '70 near their points of attachment to their connecting base 72. In this manner, the free ends of the wings will have a larger amplitude. The coil 24 of the apparatus may be connected in the output circuit of a vacuum tube, as shown in Fig. 12, or as illustrated in Fig. 1.

A sending-and receiving system is illustrated in Fig. 13, using sound as the agency of communication. The transmitting apparatus comprises a vacuum tube 74, the output circuit of which is provided with a coil 76 that'is coupled to a coil 78. The energy of the vacuum tube is thus magnetostrictively transmitted to a radiating face 80,'such as is disclosed in Figs. 7 to 12. The sound so radiated is received by the radiating face 82 of a receiving system and is magnetostrictively connected with an electromotive force in the coil 84. The coil 84 is coupled to a coil 86 of a re- Instead of the inductive coupling shown in Fig.

13, other methods of coupling used in related arts maybe employed.

If desired, the vibrator of the present invention may be sealed in a. vacuum, as in an enclosed chamber 92, Fig. 14. The chamber walls may surround the vibrator and be enclosed in the coil, without any connecting wires leading into the enclosure. I The vacuum reduces the damping and obviates rusting and accumulation of dust so that the constancy of vibration is thus preserved for precision work. Also the container eliminates the annoyance of sound radiation, who the device is used for electrical purposes in the audible range.

It will be noted that when vibrating at its fundamental frequency, the two halves 'of the centrally supported core are driven by equal and oppositely acting forces, so as to communicate practically no motion to the clamp and its base.

The apparatus is, therefore, free from one of the sources of trouble and irregularity of tuning forks,

placed. The centrally supported vibrator of the present invention is not dulled, as is a tuning fork, by itsown radiation,a very important consideration where tuned vibrators are necessary.

So well does the present vibrator balance itself about a central pivot 6 that I find that the clamp 6, 8between which the core is centrally clamped may be dispensed with and a mere rest take its place, as shown in Figs. 5 and 6, upon which the core freely rests centrally. With this arrangement the frequencies may be changed at will by merely pulling out one core and replacing it by another.

It is evident that hysteresis and eddy currents in the rod act in a detrimental manner at high frequency, and this suggests the desirability of using a tube in place of a rod. The tube may be split lengthwise further to reduce eddy cur- I find, however, that at frequencies as high as 51,000 cycles per second, which is the highest frequency yet tried, a solid nickel-steel or chromium-steel rod is highly eificient even when its diameter is as large as A,, inch, and though used in magnetizing coils that have a clearance of more than A, inch all around the rod. By diminishing this clearance and using rods of smaller diameter and shorter lengths, the upper limit of frequency can be greatly raised, and then properly constructed comminuted cores with elastic binding material will serve still further to raise the limit of available frequencies.

Other uses, also, will readily suggest themselves, such as for stroboscopic instruments.

To persons skilled in the art many applications and modifications within the spirit and scope of the invention will occur, and no effort has here been made to be exhaustive.

What I claim is:

1. A magnetostrictive mechanically-tuned alternating-current system comprising a magnetostrictive vibrator with windings magnetically cooperative with said vibrator, and a vacuum tube having plate, grid and filament, a part of said windings being in the plate-filament circuit and a part of said windings in the grid-filament circuit to produce frequency-controlled vibrations, the frequency of the alternating current of the system being constrained by the magnetostrictive vibrations of the vibrator to be substantially the same as a natural frequency of mechanical vibration of the vibrator.

2. A magnetostrictive mechanically-tuned oscillating system comprising a magnetostrictive vibrator with windings magnetically cooperative with said vibrator, and a vacuum tube having plate, grid and filament, a part of said windings being in the plate-filament circuit and a part of said windings in the grid-filament circuit to maintain, through the magnetostrictive actions of the vibrator, the frequency of the oscillations substantially constant.

3. A magnetostrictive mechanically-tuned alternating-current system comprising a magnetostrictive vibrator with windings magnetically cooperative with said vibrator, a vacuum-tube amplifier train having two or more vacuum tubes, 2. part of said windings being in the input circuit of a vacuum tube of said train, and a part of said windings being in the output circuit of a vacuum tube of said train to produce frequencycontrolled vibrations, the frequency of the alternating current of the system being constrained by the magnetostrictive vibrations of the vibrator to be substantially the same as anatural frequency of mechanical vibration of the vibrator.

4. A transformer having a magnetostrictive mechanically-tuned core, a vacuum-tube device having an output circuit and an input circuit, said transformer acting between the output and the input circuits of the vacuum-tube device to constitute a stabilized oscillator with the frequency of the oscillations constrained by the magnetostrictive vibrations of the core to be substantially the same as a natural frequency of mechanical vibration of the core, means for amplifying the output currents of said oscillator, and means for selecting harmonic constituents of current.

5. An oscillator system comprising a spacecurrent device having an anode, a cathode and an electrode for controlling the flow of space current between said cathode and said anode in accordance with variations of the potential of said electrode, and means acting magnetostrictively for controlling variations of the potential of said electrode to cause the system to oscillate.

to vibrate mechanically when stimulated magnetically by magnetostriction and to respond magnetostrictively when vibrated mechanically.

'7. An alternating-current system comprising an alternating-current circuit, a magnetomechanical vibrator,-means including a coil by which said vibrator reacts by magnetostriction upon the circuit at a predetermined frequency of the current of the system to stabilize the frequency of the system, the vibrator being adapted to vibrate mechanically when stimulated magnetically by magnetostriction and to respond magnetostrictively when vibrated mechanically, and means operatively associated with the coil for amplifying the electrical energy of the circuit.

8. The combination with an alternating-current generator, of a magnetomechanical vibrator so designed that a natural frequency of mechanical vibration of the vibrator shall be 'substantially equal to a predetermined frequency of the alternating current, and means in circuit with said generator and in operative relation with said vibrator whereby the vibrator will react upon the circuit by magnetostriction at substantially the said frequency when stimulated magnetically and to respond magnetically 'by magnetostriction when vibrated mechanically, whereby the frequency of the alternating current is maintained substantially constant.

9. A space-current device having an input circuit and an output circuit, and means including a device for coupling the circuits together through the magnetostrictive action of said lastnamed device.

10. An oscillating system comprising a spacecurrent device, a magnetostrictive vibrator, and means for operatively relating the device and vibrator through the magneto-strictive action of the vibrator to produce oscillations of substantially constant frequency.

11. An oscillating system comprising two vacuum tubes coupled together and each having an input circuit and an output circuit, and a magnetomechanical vibrator comprising a coil in the input circuit of one of the tubes and a coil in the output circuit of the other tube and having a magneto-strictive member subjected to the electromagnetic fields of the coils, the magnetostrictive member being adapted to vibrate mechanically by magnetostriction when stimulated magnetically and to respond magnetically by magnetostriction when vibrated mechanically and being designed, through the magnetostrictive action of the magnetostrictive member, to maintain the frequency of the oscillations substantially constant.

12; As oscillating system comprising two circuits, means for transferring energy from one of the circuits of the other circuit, and a magnetomechanical vibrator connected with the system to vibrate mechanically by magnetostriction 14. A system for generating oscillations comprising two circuits, means for transferring energy from one of the circuits to the other circuit, a magnetostrictive vibrator, and means for feeding back energy from the said other circuit to the said one circuit and thereby to produce in the system frequency-controlled oscillations the frequency of which is constrained by the magnetostrictive vibrations of the vibrator to be substantially the same as a natural frequency of mechanicalvibration of the vibrator, the said second-named means including a coil by which the vibrator reacts by magnetostriction at substantially the said frequency of the vibrator.

15. An oscillatory system comprising a spacecurrent device comprising three electrodes, namely, a filament, a grid and a plate, a coil connecting one of the electrodes with a second electrode, a coil connecting the said one electrode with the third electrode, and a' magnetomechanical vibraotr operatively associated with the coils for transferring energy by m'agnetostriction from one of the coils to the other coil.

16. An oscillatory system comprising a spacecurrent device comprising a filament, a grid and a plate, a coil connecting the filament and the grid,- a coil connecting the filament and the plate, the coils being wound in opposite directions, and a magnetomechanical vibrator operatively associated with the coils for transferring energy by lnagnetostriction from one of the coils to the other coil.

17. An oscillating system, comprising a driving element, a controlling element, a magnetostrictive element operatively associated with said driving element whereby said magnetostrictive element is caused to vibrate magnetostrictively, means operatively associated with said magnetostrictive element for communicating energy from the driving element to the controlling element by the magnetostrictive action of the magnetostrictive element, and means whereby the controlling element modulates the energy of the driving element.

18. An altemating-current system comprising an alternating-current circuit, a vibrator adapted to vibrate mechanically when stimulated magnetically by magnetostriction and to respond magnetostrictively when vibrated mechanically, means by which said vibrator magnetostrictive- 1y changes the equivalent impedance of the circuit, and means for utilizing the change of impedancef 19. An alternating-current system having in combination, a source of alternating current, an inductance coil connected in circuit with the source, and a tuned magnetostrictive core magnetically associated with the coil, whereby said core is caused to vibrate magnetostrictively at its tuned frequency by the current in said coil and said core reacts on the current in said coil when so vibrating to stabilize the frequency of the alternating current of the source.

. 20. A stabilizer for current frequencies comprising a magnetostrictive core inductively associated with an inductive and resistive load, said core being capable of free magnetostrictive vibration of small decrement, said vibrator reacting inductively on said load due to said magnetostrictive vibration to render its consumption of power critical as to frequency for frequencies near the free frequency of the core, and means for utilizing the variations of power consumption.

21. A stabilizer for current frequencies comprising a magnetostrictive core so associated with an inductive and resistive load as to react inductively on said load due to its magnetostrictive vibration to render its consumption of power critical as to frequency for frequencies near the free frequency of the core, and means for utilizing the variations of power consumption.

22. A constant-frequency oscillating system as claimed in claim 10 provided with means for polarizing the vibrator.

. GEORGE W. PIERCE. 

